1. Field of the Invention
The present invention relates to ware washing machines, and more particularly, to domestic or household-type dishwashers having pump assemblies which drain the wash chamber and grind food.
2. Prior Art
Many dishwashers are provided with drain pumps which drain the washing solution from the sump of the dishwashing tank and at the same time grind up or comminute relatively soft food soil particles suspended in the dishwashing solution drained from the sump. Generally speaking, these small disposers used in dishwashers have been designed to handle only "soft foods." Their purpose was primarily to reduce particle size of soft food to prevent plugging of wash arm nozzles in that type of domestic dishwasher which did not filter recirculated wash solution, and also to grind any soft food en route to a drain, in both filtered and unfiltered systems.
However, toothpicks, cherry and olive pits, cigarette filter tips, chips of glass and other hard or stringy objects also find their way into the sump. Unless they are trapped by a coarse filter covering the inlet to the disposer, they can enter the drain. Sometimes they will pass through the coarse filter and cause clogging of the system despite the presence of a soft food disposer. If either the impeller or stator of the soft food disposer is made of a plastic such as a phenolic, a hard item passing through the disposer can break parts which must then be replaced. If a coarse filter is used, it often includes labyrinthine passages to prevent long, thin objects such as toothpicks or bones from bending around short curves, while permitting passage of items such as corn, peas, cherry pits, and the like. Corn and peas can be ground in a disposer easily because they are relatively soft, but hard items such as cherry pits present a serious problem for these types of disposers.
If a flat, coarse filter were used, the openings in the filter typically would be of a size large enough such that soft items such as peas and corn would be passed to the disposer. However, a toothpick could approach the face of such a filter end first and pass straight through to cause a clogging problem. While some toothpicks are capable of cracking across the wood grain easily and being ground up by a soft food disposer, many have a long grain of such strength that they are easily bent without being broken. Whether toothpicks are trapped upstream by a coarse filter, or pass through it and cannot be cut up by the soft food disposer and are thus trapped downstream, they may create problems. Trapped toothpicks bridge across openings and capture other soil. If this occurs at the disposer itself, it may necessitate a service call. If it occurs at the coarse filter, it may result in unsatisfactory dishwashing. The reason for the latter is that trapped soil, by being unable to drain from the dishwasher at the end of any of the several discrete periods of a total dishwashing cycle, can partially break loose from time to time and get redeposited on the ware. Obviously, if this happens during the final rinse, unclean ware can result. In addition, depending on the degree to which the filter traps soil, the recirculating pump may be partially or wholly starved of a water supply.
There are several devices in the prior art which contain means to perform such draining and grinding or comminuting functions. These devices are equipped with drain and/or wash pump impellers that, either alone or in combination with stationary members, perform a comminuting function in order to reduce the oversized food and other particles that invariably would pass through coarse filters designed to retain them and cause clogging problems in the drain line or wash arm.
For example, U.S. Pat. No. 3,370,598 discloses a dishwasher having a drain pump which includes a drain impeller mounted on a common shaft with a circulating pump impeller which pumps washing solution to the spray arms. The drain impeller is positioned within a stationary shredder ring having slots spaced about its periphery through which the washing solution and food soil particles pass during both washing and draining cycles. Food soil is comminuted by the interaction of the slots of the stationary shredder ring and the blades of the impeller. The washing solution and comminuted food particles flow outwardly through the slots and downwardly to the inlet to the drain tube or line, positioned substantially below the drain impeller.
The drain pump assembly disclosed in that patent is representative of those devices which incorporate a stationary shredder ring surrounding the impeller for adapting the device to also function as a disposer. A disadvantage of this design is that, to operate efficiently as a pump as well as a disposer, the solution and comminuted particles must be subjected to pumping action after passage through the stationary shredder ring. Therefore, additional space must be provided below the impeller to accommodate the drain line inlet there as well as to expose the bottom of the impeller to the solution in order for the impeller to provide the needed pumping action.
Another disadvantage with this device is that some of the food particles are collected in the drain line downstream of the drain pump during the washing operation. Therefore, these particles make only one brief pass through the impeller prior to draining and may not be sufficiently reduced in size to eliminate a clogging problem.
U.S. Pat. No. 3,080,874 discloses a dishwasher having a waste disposer and comprising a single impeller mounted within a stationary, cup-shaped shredder ring. During draining, washing solution bearing food soil particles flows downwardly from the sump of the dishwashing tank onto the rotating impeller which propels the solution outwardly, the interaction of the shredder ring and impeller serving to comminute the food particles. A diverter valve positioned beneath the impeller directs the washing solution either to the spray arms or to a drain conduit.
While this type of device may save space in utilizing a single impeller, it possesses several disadvantages. The centrifugal pumping action of the impeller on the washing solution and particles would be substantially disrupted by the presence of the stationary shredder ring. Once the solution and particles flow through the shredder ring they are not subjected to any additional pumping action since the cup-shaped bottom of the shredder ring encloses the lower surface of the impeller. Another disadvantage is that there is no well-defined flow path for pumped fluid during either the washing or the draining modes. Fluid is pumped radially outwardly through the shredder ring, then must angle sharply downward, then sharply radially inward, then sharply upward or downward. The number of sharp turns reduces the efficiency of the pump.
There is also a disadvantage common to both of the aforementioned drain pumps. Since the components of the drain pump must be manufactured and assembled at a competitive price, these components are dimensioned to provide loose tolerances to allow for variations in size and fit. Thus, there must of necessity exist a gap between the impeller periphery and the shredder ring which may be large enough to permit the passage through the openings in the shredder ring of an elongate object, such as a section of a toothpick, without being sheared by the impeller, or only being sheared in half.
Some dishwashers include a drain pump which functions as a valve to control the fluid flow through the drain conduit. For example, U.S. Pat. No. 2,959,179 discloses a dishwasher in which the drain impeller and washing impeller are powered by a reversible motor. When the impeller is rotated in one direction, it drains the solution from the sump by functioning as an axial flow impeller, propelling the washing solution downward and outward from the sump to the drain conduit. When rotated in the opposite direction, the impeller does not permit washing solution to flow to the drain conduit but allows it to be recirculated by the blades of the washing impeller.
A disadvantage of this device is that there is no stationary member to interact with the blades of the impeller to shear food soil into smaller pieces. Therefore, hard or stringy objects suspended in the fluid being pumped by the impeller may not be comminuted at all. Furthermore, there is no means for retaining large food particles in the vicinity of the impeller until they are sufficiently comminuted to reduce the likelihood of their clogging the drain.
The device disclosed in that patent possesses a disadvantage similar to that of the devices previously discussed in that the outlet to the drain conduit is positioned directly below the drain impeller, requiring additional space.
Each of the aforementioned patents discloses a centrifugal or axial flow drain pump having an impeller which performs a cutting or grinding function to reduce the size of said particles in the fluid pumped to facilitate removal of soil during draining. However, none discloses a combination pump and comminuting impeller having radially inwardly facing grinding teeth and radially outwardly facing pumping vanes so that seeds, toothpicks, glass, and stringy objects can be sheared, and can comminute the relatively softer food particles, as well.
Accordingly, there is a need for a combination drain pump and grinding apparatus which is capable of shearing food particles to reduce their size, as well as harder material such as seeds, glass or toothpicks; which retains material in the vicinity of the comminuting activity until it is sufficiently comminuted; and which is capable of comminuting long or stringy material without the use of expensive, closely-toleranced parts.